1. Field of the Invention
The present invention relates to a magnetic disk apparatus, and more particularly to a magnetic head positioner provided in a magnetic disk apparatus for reducing the thermal off-track of magnetic heads due to variations in ambient temperature.
2. Description of the related art
First will be described a conventional magnetic head positioner for a magnetic disk apparatus with reference to FIGS. 4 and 5.
FIG. 4 is a cross-sectional view of the conventional magnetic head positioner, and FIG. 5 is a graph representing experimental data of the thermal off-track of the conventional magnetic head positioner, obtained using a prescribed ambient temperature T in the magnetic disk apparatus.
In general, the conventional magnetic head positioner of the rotary actuator type has a configuration in which two sets of bearings are fastened between a shaft and sleeve, and support rotatable arms provided with magnetic heads.
Referring to FIG. 4, the conventional magnetic head positioner has a shaft 31, two sets of bearings 32, a cylindrical sleeve 33, a magnetic head holder 34, magnetic heads 35, and arms 36.
The shaft 31, which includes a stainless steel-based material, is arranged to be stationary in the magnetic disk apparatus and functions as the center axis of rotational movement of magnetic heads 35.
The two sets of bearings 32 are arranged along their axial directions at prescribed distances on the outer peripheral side of the shaft 31.
The cylindrical sleeve 33, which includes an aluminum-based material, is fastened to the outer peripheral side of the bearings 32.
The magnetic head holder 34 is mounted on the outer peripheral side of the cylindrical sleeve 33.
The arms 36 protrude from the outer peripheral side of the magnetic head holder 34 in a horizontal direction and each arm 36 is provided with a pair of magnetic heads 35 at one end thereof. The pair of magnetic heads 35 interpose a magnetic disk 37 therebetween, respectively.
Referring to FIG. 5, the horizontal axis of the graph shows the amount of the thermal off-track at the ambient temperature T, and the vertical axis of the graph shows the disk number of the magnetic disks 37 in order from below.
According to FIG. 5, the average amount of the thermal off-track of the pair of magnetic heads 35 corresponding to each magnetic disk 37 at the ambient temperature T is approximately +2.0 .mu.m.
The above-described conventional magnetic head positioner has a following disadvantage which prevents reducing of the thermal off-track. The conventional magnetic head positioner has a configuration in which an inner peripheral surface of the bearings 32 and an outer peripheral surface of the bearings 32 are fastened, respectively, to an outer peripheral side of the shaft 31 which includes the stainless steel-based material and an inner peripheral side of the cylindrical sleeve 33 which includes the aluminum-based material.
Therefore, since the expansion or contraction of the shaft 31 and the sleeve 33 in their axial direction differ when the ambient temperature in the magnetic disk apparatus varies, this difference in the amount of expansion or contraction causes abnormal pressure variations which operate on the bearings 32.
As a result of these abnormal pressure variations, it is impossible to minimize the thermal off-track of magnetic heads 35 and improve the reliability of the magnetic disk apparatus.